1. Field of Invention
The present invention relates to an automatic balance adjusting device for an AC power supply and, more particularly, to an automatic balance adjusting device for an AC power supply that can measure the DC component of the AC power output, amplify and convert it into a current form, and send the signal through a photo coupler to a feedback control circuit to perform automatic compensation.
2. Description of Related Art
With reference to FIG. 3, a feedback control circuit (not shown but usually composed of a pulse width modulator (PWM)) is employed with the output circuit of an AC power supply to control the electrical communication among four power transistors Q1, Q2, Q3, Q4 to generate an AC output at the output terminals. The feedback control circuit obtains a feedback signal from the AC output terminals to perform compensation and to ensure stable power output.
However, when the power transistors Q1, Q2, Q3, Q4 and the feedback control circuit generate errors, the positive and negative half-cycle waves of the AC current output from the output terminals will have slight differences. In this situation, the waveforms of the positive and negative half-cycle waves are not the same. If the electrical load is inductive, the inductance in the load will be out of balance due to the integration of the voltage over time. This eventually will saturate the inductor.
Therefore, conventional AC power supplies often have different positive and negative half-cycle waveforms due to the errors in the power elements and the feedback control circuit. Providing an inductive load for a long time will saturate the inductance of the load. It is thus desirable to find a solution for such a problem.